Further to the last post, when I was in Sydney for the 46 degree new years day of 2006, The cheap and nasty Arlec split system i installed managed to cope.
I did however hose out the outdoor coils and had the gas charge spot on. It was still running a head pressure of 2400 kpa so it was pretty much at the limit but kept going. A little bit of maintenance can go a long way on super hot days.